This disclosure relates generally to a solenoid in a hydraulic pressure management system, and more particularly, to a normally rising variable force solenoid interfaced between the electronic logic and hydraulic fluid controls of such a system.
Solenoids have been used to provide hydraulic pressure management in situations where hydraulic output pressure must be independent of hydraulic supply pressure. Output pressure is proportional to the closing force of the solenoid. If the closing force can be varied, the solenoid is said to be a variable force solenoid, and if output pressure increases proportionally with applied closing force, the solenoid is said to be normally rising.
Some previous solenoid designs included springs, either as a closing force or as balance springs in combination with another closing force. However, springs are undesirable for several reasons, for example, decreased performance with wear. Moreover, decreasing the number of components to facilitate manufacture is a major concern in the industry.
One type of closing force used presently is magnetic flux applied to actuate an armature. The magnetic flux is produced by application of an electrical input current to a coil. However, the performance of these solenoids are often negatively impacted by hysteresis, a lagging in the values of resulting magnetization in a magnetic material due to a changing magnetizing force. In practical terms, hysteresis makes the solenoid less responsive to opening or closing commands by resisting movement of the armature. Furthermore, solenoids of this type must be calibrated to provide a predetermined output pressure. In the past, calibration has been a relatively arduous undertaking.
Therefore, what is needed is a normally rising variable force solenoid that is easily calibrated, and has relatively fewer components while minimizing hysteresis.